Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:
3GPP Third Generation Partnership Project
aGW access gateway
C-RNTI cell radio network temporary identifier
DL downlink (Node-B to UE)
DRX discontinuous reception
EDGE enhanced data rate for GSM evolution
eNB EUTRAN Node B
EUTRAN evolved UTRAN
GERAN GSM/EDGE radio access network
GSM global system for mobile communications
HO handover
LTE long term evolution
MAC medium access control
Node-B base station
NW network
OFDMA orthogonal frequency domain multiple access
PHY physical (e.g., layer 1 (L1))
RACH random access channel
RLC radio link control
RRC radio resource control
SC-FDMA single carrier frequency division multiple access
SCH shared channel
TA timing advance
TDM time domain multiplexing
UE user equipment
UL uplink (UE to Node-B)
UTRAN Universal Terrestrial Radio Access Network
A proposed communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently under discussion within the 3 GPP. The current working assumption is that the DL access technique will be OFDMA, and the UL access technique will be SC-FDMA.
The TA is a signal derived from the time synchronization of the UL sequence and is sent by the eNB to the UE. The UE uses the TA to advance the timing of transmissions to the eNB so as to compensate for propagation delay and, thus, time align the transmissions from different UEs within the receiver window of the eNB. By avoiding the overlapping of UL transmissions, the use of the TA allows TDM in the UL. Thus, whenever the UL access scheme is TDM based, the timing advance control information needs to be signaled from the network to the UEs. This is true for both the GERAN and E-UTRAN networks.
So long as the UE does not have any TA, the UE is normally only allowed to transmit in the UL on special allocated resources designed for this purpose. The TA can be calculated by the eNB by the UE transmitting a random access “burst” is in the UL. The random access “burst” provides a sufficiently long guard period to avoid the overlapping of uplink transmissions, but can carry only a very limited payload. Random access bursts are typically used by the UE to initiate communication with the network, when the UE does not know the TA to be used in the cell. The network's response typically contains a value for the TA to be used by the UE. Once the UE knows the TA to be used for its UL, normal communication can proceed.
Even though it can be a relatively quick process to obtain the TA information from the network, there is one case where the overall performance of the system could be increased if the UE did not have to request the timing advance to be used. More specifically, overall system performance could be improved during HO, when accessing a new cell, if the UE did not need to request the TA since not having to request and wait for the TA to be provided could potentially reduce the interruption time at HO.
A pre-synchronized handover has been standardized in GSM (3 GPP TS 44.018, V7.7.0 (2006-12) 3rd Generation Partnership Project; Technical Specification Group GSM/EDGE Radio Access Network; Mobile radio interface layer 3 specification; Radio Resource Control RRC) protocol (Release 7), see generally sub-clause 3.4.4). In E-UTRAN, a pre-synchronized handover is also being proposed (see R2-063082, Non-contention based handover execution, 3GPP TSG-RAN WG2 Meeting #55, Riga, Latvia, 6-10 Nov. 2006, Nokia).
With a pre-synchronized HO the TA to be used in the target cell is provided by the HO command sent from the source cell. There exist various means that would allow the network to assess the TA to be used in the target cell. One simple technique is when the target and source cell have co-sited antennas of the same frequency, as the TA in the target cell in this case is essentially equal to the TA in the source cell.
In GERAN, when the TA is provided in the HO command, the UE may optionally send four access bursts in the UL on the dedicated resource (CS channel) it was assigned in order to inform the target cell that is has arrived. The access bursts are sent in this case, even though the TA was provided in the HO command, due to the physical properties of the GSM L1, e.g., due to diagonal interleaving, the first four uplink slots cannot be used for speech/data transmission.